Mechanical seal assemblies are conventionally utilized on fluid handling equipment such as pumps and the like which are utilized in conjunction with highly corrosive and/or high temperature fluids, such as chemicals, petro-chemicals, steam and the like. These seal assemblies, in their most common mode of usage, are of the "inside" type in that the seal assembly is positioned in surrounding relationship to a rotatable shaft and is dispoed within a recess formed in the surrounding housing. A stationary gland is conventionally positioned adjacent the outer end of the recess and is fixedly secured to the housing, as by screws, which gland in turn nonrotatably mounts thereon the stationary annular seal member (commonly referred to as the gland insert), which insert supports the nonrotatable seal face ring. To prevent leakage between the gland and the gland insert, an annular packing or gasket is provided therebetween. This conventional arrangement is illustrated in U.S. Pat. No. 3,773,337 (owned by the assignee of this application) which, in FIG. 2 thereof, discloses a packing 23 coacting between the gland 18 and the gland insert 17. As is conventional in this industry, the packing is an axially laminated gasket constructed of a graphite material generally sold under the name "Grafoil" (trademark), but packings of other materials are utilized.
This packing as located between the gland and the insert has traditionally permitted limited leakage therepast, particularly in use situations involving high temperatures (such as in the order of 350.degree. to 400.degree. F., or above) since such use conditions have severely restricted the materials which can be successfully utilized for the packing. At the present time, most manufacturers of mechanical seal assemblies utilize a laminated graphite material for the packing in view of its capability of withstanding exposure to high temperatures and corrosive fluids. This laminated graphite packing, which is of rectangular cross-section, does operate generally satisfactorily, but nevertheless still permits limited leakage therepast due to variations (such as temperature-induced differential expansion and the like) which occur within the seal assembly within operation. However, in view of the fact that the leakage has generally been considered small, and since no better packing has been developed which overcomes the leakage problem while at the same time operating successfully under the aforementioned use conditions, manufacturers and users alike have thus tolerated the small amount of leakage past the packing.
Some attempts have been made, however, to prevent this leakage past the packing since, while the leakage has been tolerated, it is not desired. For example, in one prior attempt, a metal gasket has been used as the packing between the gland and the insert. Another prior attempt has involved the use of screws or springs for mechanically loading or compressing the packing so as to improve the sealing characteristics thereof. This latter attempt, however, is totally unacceptable when the seal assembly utilizes carbide seal rings inasmuch as it is extremely hard and hence cannot be successfully utilized with screws or similar clamping devices. Further, with respect to both of these attempts, only an extremely limited space is available for the packing, and access to this space is extremely difficult, so that both of these prior attempts have hence been unsuccessful and unsatisfactory in that the structures have been undesirably complex, and they have failed to significantly reduce the leakage past the packing.
In addition to leakage past the packing caused by differential expansion of the seal assembly components, it is believed that some of the leakage past the packing also occurs due to a general deterioration of the laminated graphite packing. Due to the lamination of the packing, it is believed that the packing initially possesses at least limited resiliency, particularly in its axial direction, so that the end faces thereof initially maintain a tight sealing contact with the opposed axial faced formed on the insert and the gland. However, during continued operation of the mechanical seal assembly, the exposure of the packing to the hot fluid causes the packing to become saturated, and also causes the packing to lose some of its compressibility, whereby leakage occurs through and/or around the packing.
Accordingly, it is an object of this invention to provide an improved mechanical seal construction which employs an improved packing arrangement between the gland and the insert, which packing arrangement still permits successful utilization of the seal assembly with corrosive and/or high temperature fluids, while resulting in a substantial reduction in the amount of leakage past the packing during long-term operation of the seal assembly.
In the improved seal assembly of this invention, the improved packing arrangement again utilizes a laminated graphite packing of substantially rectangular cross-section and positioned within a suitable annular recess formed between the gland and the insert. However, one of the annular seats for the packing, such as the inner annular surface defined on the insert, is provided with a slightly tapered configuration so that the continual urging of the insert toward the gland, coupled with the tapered configuration of the inner seating surface, causes the laminated graphite packing to be continuously compressed and reseated against the inner and outer seating surfaces, whereby leakage of corrosive and/or high temperature fluid past the packing is greatly reduced. In fact, experimental testing of this improved packing arrangement indicates that the leakage of fluid or product past the packing is reduced by several orders of magnitude in comparison to the leakage which occurs past the laminated graphite packing when same is seated in a conventional manner between opposed concentric inner and outer seating surfaces as defined on the insert and gland respectively.
Other objects and purposes of the invention will be apparent upon reading the following specification and inspecting the accompanying drawings.